Question: Which of the following numbers is a factor of 72? ${5,6,10,11,13}$
Answer: By definition, a factor of a number will divide evenly into that number. We can start by dividing $72$ by each of our answer choices. $72 \div 5 = 14\text{ R }2$ $72 \div 6 = 12$ $72 \div 10 = 7\text{ R }2$ $72 \div 11 = 6\text{ R }6$ $72 \div 13 = 5\text{ R }7$ The only answer choice that divides into $72$ with no remainder is $6$ $ 12$ $6$ $72$ We can check our answer by looking at the prime factorization of both numbers. Notice that the prime factors of $6$ are contained within the prime factors of $72$ $72 = 2\times2\times2\times3\times3 6 = 2\times3$ Therefore the only factor of $72$ out of our choices is $6$. We can say that $72$ is divisible by $6$.